Two instant messaging (IM) models currently exist—session based and page mode. Session based IM requires that a dialogue be established between two endpoints prior to the transmission of messages. If an IM service permits a user to be logged into only a single client—e.g., endpoint—at any one time, a session can be established “under the covers” without any required interaction with or involvement of the user. A major drawback to pure session based IM is that, while suitable for endpoint-to-endpoint IM, it does not work when a user is logged into multiple client endpoints. Stated another way, any IM service that allows users to log into multiple client endpoints at once cannot be based on pure session based IM.
For example, if a session based IM service permits a user to log into multiple endpoints at once, then a target endpoint for that user must be selected when the session is initiated. The target endpoint can either be selected by the network or the user. If the network selects the endpoint, there is no way to guarantee that the selected endpoint is the appropriate endpoint—e.g., the endpoint at which the user is located. If the user selects the endpoint, then either the user is required to set complex rules for IM routing that reside in the network, or the session invitation must be sent to all endpoints, and the user must actively “Accept” the IM session. This is similar to the experience of phone users who must accept a call before a voice session can begin.
The active acceptance requirement of an IM session is counterintuitive and results in a loss of several highly desired user experiences. One desired user experience is that IM users expect to receive messages without having to acknowledge the received messages. Additionally, IM users expect to be able to receive multiple messages without having to actively participate in the session. For example, the user could be away or just choose to not reply at that moment and still expect that the other party be able to send IMs at will. A drawback with requiring the active acceptance of an IM session is that, if a user is away or is not able to acknowledge, the free flow of IM that users typically expect, and have become accustomed to, is not possible.
An alternative to session based IM is IM page mode where all messages are delivered to all registered endpoints. Therefore, with IM page mode, a user is allowed to be logged into multiple endpoints. But, support of multiple registered endpoints has several drawbacks. First, as discussed above, the desirable properties provided by session based messaging are not available because of the support of multiple endpoints. Second, the user experience is poor as one endpoint will be engaged in a 2-way IM session and all other endpoints will simply reflect the list of incoming messages because all the messages that the user receives are always delivered to all of the user's endpoints.
Accordingly, an IM model that supports multiple user endpoints while providing the user experience associated with session based IM will have significant utility.